Vehicle fuel economy may be improved by selectively stopping and starting the engine of a vehicle. An engine may be stopped while the vehicle is in heavy stop-and-go traffic or at stop lights, for example. Stop/start vehicles were initially introduced in manual transmission vehicles because few controls were required beyond the capability to sense a driver's foot on a clutch pedal and the gear shift position. In such systems, the operator controlled the vehicle launch after an engine start by releasing the brake and engaging first gear and the clutch. This arrangement allowed an engine controller to concentrate on controlling the engine in specific modes (e.g., start mode, idle speed control mode or engine torque control mode) while the driver controlled wheel torque by way of the manual clutch.
Recently, however, start/stop engine operation has been proposed for engines coupled to automatic transmissions. Starting of an engine coupled to an automatic transmission may be initiated while the vehicle is in gear. In such vehicles, the operator has less capacity to control the amount of engine torque that is transmitted to vehicle wheels when the engine is restarted in gear as compared to manual transmission vehicles because the driver may not have direct control over transmission clutches. Further, accurate engine speed control during engine starts may be desirable so that speed dependant torque transfer characteristics of a torque converter coupled to the engine crankshaft and transmission input may have less affect on wheel torque, thereby improving vehicle launching. Consequently, an engine controller may be assigned more authority over engine control modes (e.g., start mode, idle speed mode or engine torque control mode) and the amount of engine torque that is transmitted to vehicle wheels. Nevertheless, it may still be desirable for an engine controller to respond to driver inputs during an engine start so that the driver's intentions may be followed. For example, it may be desirable to provide additional torque to vehicle wheels and transition directly from start mode to torque control mode, thereby bypassing idle speed control mode when a driver immediately depresses the throttle after releasing the brake pedal. Thus, there is a need for a method to control engine speed and torque of a stop/start vehicle while also responding to driver demands.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for improving engine starting. In one embodiment of the present description, a method for starting an engine and controlling engine speed is described. The method comprising: automatically starting an engine; injecting fuel into at least one cylinder during the automatic start, the injection of fuel during a cycle of a cylinder and comprising a first injection and a second injection; and transitioning to injecting fuel once during a cycle of the cylinder in response to a pressure of an intake manifold when a speed of the engine exceeds a threshold.
Engine starting can be improved by transitioning between engine control modes in response to engine speed and intake manifold pressure. In particular, during a start of an engine coupled to an automatic transmission that is in gear, fuel injection mode may be controlled to regulate engine torque in response to manifold pressure when engine speed exceeds a threshold. For example, if during an engine restart, an operator does not immediately depress an accelerator pedal, the engine speed may reach a desired speed before intake manifold pressure drops below a desired level. A split injection during this period may lower the combustion torque and improve engine combustion stability at these reduced combustion torque levels. However, once the intake manifold pressure drops below a desired level, fuel injection may be transitioned to a single injection mode where engine speed and torque may be controlled by way of spark or air flow throttling.
The present description may provide several advantages. Specifically, the approach may improve engine speed control for an engine that is coupled to an automatic transmission and that is started while in gear because the approach may provide improved engine torque control robustness and combustion at lower engine torque levels, than was previously available with conventional single fuel injection methods during an engine start. Further, the approach may reduce engine emissions after the engine operates in a stable combustion mode. Further still, the approach may provide improved transitions between engine modes at engine start by considering engine operating conditions beyond engine speed.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.